German patent application No. 42 26 749 discloses a method of wherein, signals representative of the longitudinal acceleration a.sub.x, the vehicle speed in a longitudinal direction v.sub.x, transverse acceleration a.sub.y, and yaw velocity .psi. are sent to a calculating device. At least the sideslip angle .beta. is derived on the basis of these measured quantities in the calculating device by using a vehicle model. In the course of the calculating operation, pitching and rolling motions of the vehicle are assumed to have an insignificantly low value in order that the rotational speeds about the longitudinal and transverse axis of the vehicle can be set equal zero and a complex equation system is thus simplified. Likewise the transverse vehicle acceleration is assumed to adopt the value which is measured by transverse accelerometers fixed to the vehicle so that lateral road surface inclinations are also assumed to be transverse accelerations.
This automatically causes mistakes in the calculation of the sideslip angle. It is therefore impossible to ensure that the control will lead to the desired driving behavior even when driving on slopes without taking the transversal inclination into account.
In order to ensure stability and good quality of yaw torque control even with road transversal inclinations and/or with a rolling motion of the vehicle, transversal inclination identification is necessary. The transversal inclination identification is performed by calculating the transversal inclination angle. When a transversal inclination is identified, the controller, i.e., the calculating device, can be set to counteract transversal inclinations vigorously.
An object of the present invention is to provide a method of the above-mentioned type which permits distinguishing between a transversal inclination of the vehicle and a genuine transverse acceleration of the vehicle and indicating the respective values thereof.
This object is achieved by the present invention wherein the calculation of the transversal inclination angle is based on a transformation of coordinates.
The value measured by the transverse accelerometer fixed to the vehicle is related to a value of the ground-related transverse acceleration which is calculated from other sensor signals. `Ground-related` implies that the z-axis of the coordinate system extends in the direction of gravity, and the x-axis and y-axis extend vertically thereto in the longitudinal and transverse direction of the vehicle.
The ground-related transverse acceleration of the vehicle can be calculated from a measured or calculated yaw velocity and the longitudinal vehicle speed or from the individual wheel speeds of one right and one left vehicle wheel each.
If desired, part of the transversal inclination angle can be assigned in a simple way as roll angle by multiplying the measured vehicle-related transverse acceleration with a vehicle-specific load-responsive factor. This factor is preferably determined one time by test measurements and stored in the calculating device in the vehicle.